The invention relates to a device for stabilizing the temperature of the transmission oil of a motor vehicle with a liquid-cooled engine, whose coolant, recoolable in a radiator, can be conducted as a function of temperature through a heat exchanger that can likewise be traversed by the transmission oil.
If it is necessary in motor vehicles to cool the oil of a transmission provided in the vehicle drive train (manual transmission, automatic transmission with hydraulic torque converter, or axle drive), an air/oil heat exchanger is usually provided for that purpose. In addition, it is known from German Patent document DE 32 01 443 A1 to heat the transmission oil more rapidly following a cold start of the vehicle by guiding the oil through an oil/coolant heat exchanger that is also traversed by the coolant of the engine that drives the vehicle. Since the coolant of a liquid-cooled engine, following a cold start of the motor vehicle, is heated more rapidly than the transmission oil, the transmission oil can thus be brought more rapidly to its optimum operating temperature. If these two systems were combined with one another, so that the transmission oil would be warmed more rapidly and the transmission oil could be recooled if necessary, this would involve a considerable expense since at least two heat exchangers would be required for the transmission oil. A high regulating cost is also required for this purpose if a desired oil temperature is to be reached or set.
The goal of the present invention is to describe improvements in this regard.
To achieve this goal, provision is made such that the coolant flow supplied to the transmission oil/coolant heat exchanger is miscible in a thermostatic valve from recooled as well as non-recooled coolant. Advantageous embodiments and improvements are further described herein.
According to the present invention, a single heat exchanger suffices for the transmission oil in order to control the temperature of the latter if required, in other words to heat it more rapidly following a cold start and to recool it later, with the engine coolant also being conducted through this heat exchanger at a temperature that can be controlled. For this reason, a thermostatic valve is provided that sets the temperature of the coolant stream flowing through the heat exchanger. This temperature adjustment is performed by controlled mixing of recooled and non-recooled coolant from the engine. As already mentioned above, coolants with different intrinsic temperatures are available. Firstly, the coolant derived from the engine can be used, said coolant being relatively warm, and secondly the coolant recooled in the vehicle radiator can be used, said coolant having an even lower temperature. By suitable mixing of these two coolant volumes, in other words by suitable mixing of the recooled and non-recooled coolant, a desired coolant temperature can be set in the coolant/transmission oil heat exchanger that allows for the desired transmission oil temperature control.
Preferably, provision can be made such that the thermostatic valve for mixing the recooled and non-cooled coolant is controlled by the temperature of the transmission oil. This ensures the fastest possible regulation, as well as the most reliable, since the temperature of the medium that controls the temperature of the transmission oil, namely the temperature of the coolant, is set as a function of the result of the temperature control, i.e. by the temperature of the transmission oil.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.